Author: Armin Rigo <[email protected]>
Branch:
Changeset: r63785:ffe6fdf3a875
Date: 2013-05-01 19:33 +0200
http://bitbucket.org/pypy/pypy/changeset/ffe6fdf3a875/
Log: A version of zip() specialized for two arguments. It is more than
four times faster (tested with lists of 10 items).
diff --git a/pypy/module/__builtin__/app_functional.py
b/pypy/module/__builtin__/app_functional.py
--- a/pypy/module/__builtin__/app_functional.py
+++ b/pypy/module/__builtin__/app_functional.py
@@ -203,7 +203,29 @@
Return a list of tuples, where each tuple contains the i-th element
from each of the argument sequences. The returned list is truncated
in length to the length of the shortest argument sequence."""
- if not sequences:
+ l = len(sequences)
+ if l == 2:
+ # This is functionally the same as the code below, but more
+ # efficient because it unrolls the loops over 'sequences'.
+ # Only for two arguments, which is the most common case.
+ seq0 = sequences[0]
+ seq1 = sequences[1]
+ iter0 = iter(seq0)
+ iter1 = iter(seq1)
+ hint = min(100000000, # max 100M
+ operator._length_hint(seq0, 0),
+ operator._length_hint(seq1, 0))
+
+ with _ManagedNewlistHint(hint) as result:
+ while True:
+ try:
+ item0 = next(iter0)
+ item1 = next(iter1)
+ except StopIteration:
+ return result
+ result.append((item0, item1))
+
+ if l == 0:
return []
# Gather the iterators and guess the result length (the min of the
diff --git a/pypy/module/__builtin__/test/test_zip.py
b/pypy/module/__builtin__/test/test_zip.py
--- a/pypy/module/__builtin__/test/test_zip.py
+++ b/pypy/module/__builtin__/test/test_zip.py
@@ -13,6 +13,12 @@
def test_one_list(self):
assert zip([1, 2, 3]) == [(1,), (2,), (3,)]
+ def test_two_lists(self):
+ # uses a different code path
+ assert zip([1, 2, 3], [3, 4, 5]) == [(1, 3), (2, 4), (3, 5)]
+ assert zip([1, 2, 3], [3, 4]) == [(1, 3), (2, 4)]
+ assert zip([1, 2], [3, 4, 5]) == [(1, 3), (2, 4)]
+
def test_three_lists_same_size(self):
assert zip([1, 2, 3], [3, 4, 5], [6, 7, 8]) == (
[(1, 3, 6), (2, 4, 7), (3, 5, 8)])
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